Process for the manufacture of polarizing materials



H. H v xa Brasserie baamh Rmm Patented July 14, 1. 7X 7 L 2 2 9 712 UNlTED oiAihs' tA'l'liNl' ur'FlCE PROCESS FOR THE MANUFACTURE OF l r POLARIZING MATERIALS X x i Edwin H. Land, Wellesley Farms, and Cutler D. West, Cambridge, Mass, assignors, by mesne assignments, to Polaroid Corporation, Dover, Del., a corporation of Delaware No Drawing. Application December 4, 1937, Serial No. 178,152

8 Claims. (Cl. 260-284) This invention relates to a new and improved patent to Land, No. 1,951,664, there is disclosed process for the manufacture of light-polarizing a process for the manufacture of colloid-like materials, and more specifically to a new and crystals of herapathite. improved process for the manufacture of such This application relates primarily to methods materials formed from a suspension of a multiof control whereby the crystals or particles of plicity of minute and preferably colloid-like the herapathite-like material employed with a crystals of a herapathite-like material in a viscous suspending medium in the production of viscous, light-transmitting supporting medium. light-polarizing sheets or films may be invariably An object of the invention is to provide a and uniformly produced of a predetermined size method for the production of a viscous suspen- 10 nd b a d i is a p y Object of this sion of the character described wherein the forvention to teach the art the bounds or limits mation of the suspended herapathite-like crystals within which the properties or the concentrations is so controlled as to produce crystals of a shape of the substances entering into the process may or habit such that they may respond to mechanbe safely varied without appreciable alteration ical stress applied to the suspending medium in the characteristics of the product formed. whereby an orientation of the polarizing axes of In the sp ific ion r ferenc will be made the crystals may be secured within the suspenprimarily to the production of herapathite cryssion by subjecting the suspension to such a stress. tals. By this is meant crysta s which mayfic A still further object of the invention is to prorepresented generally by the chemical formula vide a method of the character described whereby Q.%HzSO4. HI.I, wherein Q denotes the quinine the size of the crystals of the herapathite-like molecule C20H2iO2N2. Such crystals may be consubstance may be controlled so that the polarsidered as consisting of five comp izing body formed from the Viscous suspension q hydrogen Sulfate i011, iodide 1011, may transmit light without appreciable scatand. iodine. In place of the sulfa e i011 y tering. tal may comprise a selenate ion, which may be Other objects of the invention are to provide obtained, fo p f o Selenio ac d or methods for the control of some or all of the quinine biselenate. C ystals comp a following factors in the production of a viscous selenate ion have the same opticalproperties a8 suspension of herapathite-like crystals of the those comprising a sulfate ion. Speaking gencharacter described: erally, the precipitate may be formed by adding 1. The acidity of the solution from which the to a solution containing so of these P crystals are precipitated, nents another solution containing the remaining 2. The concentration within the solution of mp nt e character f the p p at soluble metallic salts. with reference to the crystal size and to the crys- 3, Th e tr t n it t crystal-formtal form or habit will be affected by the relative ing 1 ti of the i did i concentration of each of these five components. 4. The characteristics of the medium Within It Will be readily app that y e pt o which th precipitate i thro d define the variables in such a precipitation 5. The properties of the viscous suspending process involves omp ons.

medium into which the precipitate is introduced. Suitable viscous suspending di f u e in Other objects of the invention will in part be the manufacture Of 8110b 9, material 8S those obvious and will in part appear hereinafter. disclosed in the above mentioned patents y The invention accordingly comprises the sevcomprise a substance from the g p Consisting eral steps and the relation of one or more of such of the cellulose esters or from the g p of steps with respect to each of the others thereof vinylic resins, miXed W vo e vent. For

which will be exemplified in the process hereinexample, a suitable suspend um may be after disclosed, and the scope of the application formed from an acetone-soluble cellulose acetate of which will be indicated in the claims. (51 to 55% acetic acid) and a volatile solvent,

In the patent to Land and Friedm N such as a mixture of three volumes of ethyl 1,918,848 there is disclosed alight-polarizing body 5 acetate with one volume of methanol. Other comprising a set suspension of oriented crystals suitable cellulose esters are cellulose nitrate, of herapathite or of a similar polarizing subcellulose acetate butyrate, cellulose acetate stance in a light-transmitting plastic. Such a c e, Cellulose acetate propionateb e material as is disclosed in' this patent is now being viny i r ins for se in he form tion of the sold under the trade name Polaroid. In the 55 viscous suspending medium are polystyrene, polychoice of the solvent may be allowed. Where the.

suspending medium for the herapathite like crystals is to comprise cellulose acetate, it is recommended that the preferred solvent, as specified above, be employed. Where the suspending medium comprises the vinyl resins, for example, the volatile solvent may comprise a chlorinated hydrocarbon, such as carbon tetrachloride or chloroform, or an aromatic hydrocarbon, such as benzene.

This invention contemplates the formationof needle-like or fibre-like crystals or particles of a herapathite-like material and the incorporation of such particles in a viscous suspending medium. The form or habit of the particles is important, for orientation of the multiplicity of particles within-the medium is obtained by stressing the medium, as for example by stretching, extruding, flowing, pouring, or rolling it, i. e., by exerting upon the suspended particles a mechanical force which tends to cause a physical orientation of the needle-like axes of the particles in the direction a of flow of the suspending medium. It is accordingly important that the precipitation of the herapathite be in the form of needle-like or fibrelike particles, and plate-like crystals are to be avoided.

It has been found convenient to precipitate the crystals of herapathite in the solvent which is to be employed to dissolve the plastic comprising the viscous suspending medium. Where such a technique is followed, care should be taken to avoid the formation of herapathite crystals in a solvent comprising acetone in lieu of ethyl acetate, for the acetone-containing solvent has been found to give rise to the formation of plate-like crystals of herapathite which fail to orient optically when the medium in which they are suspended is subjected to a mechanical stress of the type indicated.

In the formation of the precipitate of herapathite care should be taken to avoid an excess of alkali or acid, or else the desired precipitate will not form. A satisfactory acidity is found to be present when the ratio of quinine to hydrogen ion is 1 to 2. This ratio is that found in the herapathite crystal and is readily obtained when the crystal is formed from quinine bisulfate or from quinine dihydriodide, in the absence of any other hydrogen ion source. Where the herapathite-like precipitate is produced from quinine sulfate it should preferably be produced in the presence of a hydrogen ion source, such that the preferred ratio of quinine to hydrogen ion present is not exceeded.

It has been found that where the ratio of quinine to hydrogen ion rises to 1 to 1, the herapathite crystalline precipitate will not form, and where the ratio falls substantially below 1 to 2, no precipitate is obtained. Accordingly the concentration of quinine to hydrogen ion in the crystal-forming solution should preferably be approximately 1 to 2, should be less than 1 to 1, and should not fall substantially below 1 to 2.

In the formation of the herapathite precipitate an excess of either quinine bisulfate or quinine dihydriodide is tolerated, while an excess of quinine or an excess of sulphuric acid of hydriodic acid is not tolerated.

The concentration of the iodide ion in the crystal-forming solution may satisfactorily be controlled by introducing into the solution a soluble metallic iodide in the desired concentration. Suitable iodides may comprise ammonium iodide, potassium iodide, sodium iodide, magnesium iodide, barium iodide, arsenic triiodide, antimony triiodide and stannic iodide. Each of these compounds is a methanol soluble metallic iodide and suitable where the crystals are to be formed in the preferred ethyl acetate-methanol mixture. It has been found that where the soluble metallic iodide is present in the'crystal-forming solution in such concentration as to give only an iodide ion concentration equal to that of general formula for herapathite the crystals formed by precipitation from the solution are of a form or habit unsuitable for use in the formation of a polarizing sheet from a viscous suspension of the character hereinbefore described. It has been found necessary to increase the concentration of the iodide ion to from one and one-half to three times the concentration of the iodide ion obtained from the herapathite formula. For example, where the iodide ion is to be obtained from ammonium iodide, potassium iodide, sodium iodide, magnesium iodide, or barium iodide, or from ferrcus iodide, substantially three times the calculated concentration of soluble metallic iodide should be employed to produce herapathite crystals of the preferred habit, while if the iodide ion is to be obtained from the other soluble metallic iodides mentioned approximately one and onehalf times the calculated concentration of those salts should be employed.

If, however, an excess of soluble metallic iodide be employed over the quantities just specified, there is great danger that no herapathite precipitate whatever will be formed. Accordingly the control of the iodide ion concentration in the crystal-forming solution should be maintained within a range of from substantially one and one-half times the calculated concentration to not greatly in excess of three times the calculated concentration, depending in part at least upon the source of the iodide ion, as indicated above,

Inasmuch as the iodine-containing solutions and crystals employed and formed in the process of this invention react with most metals, and more particularly with iron, care should be taken to carry out the process of crystal formation and incorporation of the crystals in the plastic suspending medium and the formation of the polarizing sheet therefrom in containers and apparatus which are relatively inactive with respect to the solutions and suspensions employed. It has been found that containers lined with chromium or with tin are satisfactory, as are also glass, fibre, porcelain and the like. It will be apparent that the control instructions given herein are based upon a process carried out in connection with apparatus which is inactive or substantially inactive with respect to the solutions and mixtures employed.

Where quinine dihydriodide is employed, the desired excess of the iodide ion over that present in the theoretical formula may be obtained by employing an excess of quinine dihydriodide.

It should be noted that methanol insoluble iodides are unsuitable in the preferred process, as are also organic compounds containing iodine,

found not to yield the iodide ion in solution.

Wide variations in the concentration of the iodine and the sulfate ion or the selenate ion within the crystal forming solution may be tolerated without impairing the properties of the herapathite precipitate formed. Speaking generally, however, a substantial excess of iodine over the calculated amount should be avoided because it remains dissolved in the suspending medium after the solvent has volatilized, and while it does not add to the polarizing properties of the sheet, it impairs its light transmission and makes the sheet dark and brownish. In fact the preferred herapathite crystal of the present invention may be produced from the solution with an iodine deficiency therein.

If the quinine, the hydrogen ion and the iodide ion are controlled Within the limits indicated above, a precipitate of minute. needle-like or fibre-like crystals of herapathite may be obtained in, for example, an ethyl acetate-methanol mixture, and the mixture and precipitate may be suitably mixed with a plastic, such for example as cellulose acetate, to form a viscous suspension of needle-like polarizing particles in a transparent plastic, uniformly and regularly without substantial variation in the size or habit of the crystal or in the properties, either physical or optical, of the polarizing sheet formed from the viscous suspension.

A preferred method of combining the components of the theoretical herapathite formula in the desired ratio and with the desired control is to employ quinine bisulfate, a soluble metallic iodide, and iodine. The precipitate may be formed by mixing a solution of quinine bisulfate, for example, with a solution of the soluble metallic iodide and iodine, the components of each solution being calculated within the control limits previously outlined. For example, a methanol solution of quinine bisulfate may be added to a solution of the soluble metallic iodide and iodine in a methanol-ethylgzet ate mixture. It is to be understood, however, that other methods of forming the desired precipitate may be em-- ployed. For example, the soluble metallic iodide and iodine solution may first be added to the cellulose acetate and the quinine bisulfate solution added later during mixing. If this procedure is followed the herapathite crystals tress Pieerente ch .for example as iodoform, which have been are formed within the viscous suspending mea dium.

If ferrous iodide is employed as the source of the odide ion it should be noted that each ferrous ion will reduce one iodine atom to iodide ion and calculations should be made accordingly.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A process for the production of minute, needle-shaped, herapathite crystals, comprising forming, in a solvent of the class consisting of carbon tetrachloride, chloroforn1, ;benzene and a mixture of ethyl acetate and methanol, a so-' lution of quinine, hydrogen ions, iodide ions, ions of the class consisting of the sulphate ion and the selenate ion, and iodine, the ratio of the number of quinine molecules to the number of hydrogen ions being less than 1 to 1 and not substantially below 1 to 2, the amount of iodide ions being substantially in excess of the amount thereof as calculated from the empirical formula for herapathite, the amount of iodine being no greater than the amount thereof as calculated from the empirical formula for herapathite, and allowing a precipitate of needle-shaped crystals to form,

2. In a process of producing minute, needleshaped crystals of herapathite by precipitation from a solution of quinine, hydrogen ions, iodide ions, ions of the class consisting of the sulphate ion and the selenate ion, and iodine, in a solvent comprising substantially three parts of ethyl acetate and one part of methanol, the Steps comprising introducing into the solution quinine molecules and hydrogen ions in a ratio of less than 1 to l and not substantially below 1 to 2, and introducing into the solution iodide ions in an amount substantially in excess of the amount thereof as calculated from the empirical formula for herapathite, while maintaining the amount of iodine substantially no greater than the amount thereof as calculated from the empirical formula for herapathite.

3. A process for the production of minute, needle-shaped, herapathite crystals comprising forming, in a solvent comprising substantially three parts of ethyl acetate and one part of methanol, a solution of quinine, hydrogen ions, iodide ions, ions of the class consisting of the sulphate ion and the selenate ion, and iodine, the ratio of the number of quinine molecules to the number of hydrogen ions being less than 1 to 1 and not substantially below 1 to 2, the amount of iodide ions being substantially in excess of the amount thereof as calculated from the empirical formula for herapathite, the amount of iodine being no greater than the amount thereof as calculated from the empirical formula for herapathite, and allowing a precipitate of needle-shaped crystals to form.

4. In a process of producing minute, needleshaped crystals of herapathite by precipitation from a solution of quinine, hydrogen ions, iodide ions, ions of the class consisting of the sulphate ion and the selenate ion, and iodine, in a solvent of the class consisting of carbon tetrachloride, chloroform, benzene and a mixture of ethyl acetate and methanol, the steps comprising introducing into the solution quinine molecules and hydrogen ions in a ratio of less than 1 to 1 and not substantially below 1 to 2, and introducing into the solution iodide ions in an amount substantially in excess of the amount thereof as calculated from the empirical formula for herapathite, while maintaining the amount of iodine substantially no greater than the amount thereof as calculated from the empirical formula for herapathite.

5. In a process of producing minute, needleshaped crystals of herapathite by precipitation from a solution of quinine, hydrogen ions, iodide ions, ions of the class consisting of the sulphate ion and the selenate ion, and iodine, in a solvent of the class consisting of carbon tetrachloride, chloroform, benzene and a mixture of ethyl acetate and methanol, the steps comprising introducing into the solution quinine molecules and Search Room 

